authorSTREAM desktop is pretty simple to use and contrary to SlideFinder their image and video search interface seems to be a part of PowerPoint software itself. Here's a video, in which Harman Singh the CEO of authorGEN(Company behind authorSTREAM) demonstrates authorSTREAM desktop:

Using authorSTREAM Desktop

authorSTREAM's closest competitor SlideShare too allows you to embed YouTube videos in presentations uploaded on their website. You have to edit your presentation after your presentation gets converted on SlideShare. This video is inserted as a separate flash file after slide number selected by you. So if you download the PowerPoint file from SlideShare, there will be no slide having YouTube video.

YouTube videos embedded using authorSTREAM desktop not only play fine on authorSTREAM but they even work fine in PowerPoint slide show. This means you can share PowerPoint presentations having YouTube embed inserted using authorSTREAM desktop, through emails too. You can have text as well as YouTube video on same slide and next/ back arrows on player also work fine. See it yourself below:

Justin Ezarik

Uploaded on authorSTREAM by caliber | Upload your own presentation

You can insert YouTube videos in PowerPoint files manually too as explained here and authorSTREAM handles that too.

authorSTREAM recently changed their tagline to "Do More with PowerPoint" and their recent updates for PowerPoint to video, Channels, and authorSTREAM desktop validates that.